package com.npr.util;

import org.apache.commons.lang3.CharUtils;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

@Component
public class SensitiveFilter {

    private static final Logger logger = LoggerFactory.getLogger(SensitiveFilter.class);
    //替换符
    private static final String REPLACEMENT ="***";
    //根结点
    private TrieNode rootNode = new TrieNode();
    @PostConstruct
    public void init(){

        try (
                InputStream is = this.getClass().getClassLoader().getResourceAsStream("sensitive-words.txt");
                BufferedReader reader = new BufferedReader(new InputStreamReader(is));
                ){
            String keyword;
            while((keyword = reader.readLine())!=null){
                //添加到前缀树
                this.addKeyword(keyword);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    //将一个敏感词添加到前缀树中
    private void addKeyword(String keyword){
        TrieNode tempNode = rootNode;
        for(int i=0;i<keyword.length();i++){
            char c = keyword.charAt(i);
            TrieNode subNode = tempNode.getSubNode(c);
            if (subNode==null){
                //初始化子节点
                subNode = new TrieNode();
                tempNode.addSubNode(c,subNode);
            }
            //指向子节点，进入下一轮循环
            tempNode = subNode;
            //设置结束标识
            if(i==keyword.length()-1){
                tempNode.setKeywordEnd(true);
            }
        }
    }

    /**
     * 过滤敏感词
     * @param text 待过滤的文本
     * @return 过滤后的文本
     */
    public String filter(String text){
        if(StringUtils.isBlank(text)){
            return null;
        }
        //指针1
        TrieNode tempNode = rootNode;
        //指针2
        int begin = 0;
        //指针3
        int position = 0;
        //结果
        StringBuilder sb = new StringBuilder();

        while (position<text.length()){
            char c = text.charAt(position);
            //跳过符号
            if(isSymbol(c)){
                //若指针1处于根结点，将此符号计入结果，让指针2向下走一步
                if(tempNode==rootNode){
                    sb.append(c);
                    begin++;
                }
                //无论符号在开头或中间，指针3都向下走一步
                position++;
                continue;
            }
            //检查下级结点
            tempNode = tempNode.getSubNode(c);
            if(tempNode == null){
                //以begin开头的字符串不是敏感词
                sb.append(text.charAt(begin));
                //进入下一个位置
                begin++;
                position=begin;
                //重新指向根结点
                tempNode = rootNode;
            }else if(tempNode.isKeywordEnd()){
                //发现敏感词，将begin~position字符串替换掉
                sb.append(REPLACEMENT);
                //进入下一个位置
                begin = ++position;
                //重新指向根结点
                tempNode = rootNode;
            }else{//检查下一个字符
                position++;
            }
        }
        //将最后一批字符计入结果
        sb.append(text.substring(begin));
        return sb.toString();
    }
    //判断是否为符号
    private boolean isSymbol(Character c){
        //0x2E80~0x9FFF是东亚文字范围
        return !CharUtils.isAsciiAlphanumeric(c) && (c<0x2E80||c>0x9FFF);
    }
    //前缀树结点
    private class TrieNode{
        //关键词结束标识
        private boolean isKeywordEnd = false;
        //子节点(key是下级字符，value是下级结点)
        private Map<Character,TrieNode> subNodes = new HashMap<>();
        //添加子节点
        public void addSubNode(Character c,TrieNode node){
            subNodes.put(c,node);
        }
        //获取子节点
        public TrieNode getSubNode(Character c){
            return subNodes.get(c);
        }

        public boolean isKeywordEnd() {
            return isKeywordEnd;
        }

        public void setKeywordEnd(boolean keywordEnd) {
            isKeywordEnd = keywordEnd;
        }
    }
}
